Closures for metal beverage containers are generally of a circular shape with a flanged perimeter. The flanged perimeter is used in attaching the closure to a can body through a seaming operation. To aid the integrity of the seal thus formed between the can body and the closure, it is a common practice to apply a bead of sealant within the flanged perimeter during manufacture of the closure.
One problem which arises in this manufacturing operation is the curing or drying of such sealants. To facilitate handling of the closures after the application of a sealant, the closures are often accumulated into a columnar stack and transported to the next operation through appropriate trackwork. When the closures are in such a stacked condition, it is difficult or impossible to direct energy waves such as heat or moving air across the sealant to accelerate the drying process. The flange, in combination with the adjacent stacked closure, effectively shields the sealant from outside influences.
When the sealant is of the solvent-based type, this is not a severe problem. Even in the stacked condition, the volatile solvent quickly evaporates and within 24 to 48 hours the sealant is acceptably dry for application of the closure to a can body.
Recently there has been an increased interest in the use of water-based sealants in the container industry. These sealants present much greater difficulty in quick and effective drying. Very slow drying takes place and it may take up to 10 days for the sealant to dry to an acceptable state for application of the closure to a can body.
Prior to the present invention, the achievement of practical drying times for water-based sealants required complicated apparatus to unstack the closures and transport them, one at a time, through a hot air blowing station thereby allowing streams of air to directly impinge the sealant and effectively dry it. Apparatus used in such an operation has many drawbacks, mainly due to its complexity, high cost, and expansive floor space requirements.